The invention relates generally to turbine runners and to turbines incorporating such turbine runners, which are well suited for use as hydraulic turbines for hydroelectric power generation.
The hydraulic turbine is an element of turbomachinery that efficiently converts hydraulic energy into mechanical energy. Hydraulic turbines are included in river dams to generate hydroelectric power.
There are a number of types of conventional turbine wheels, or runners that are utilized in turbines for hydroelectric power generation. Two examples of conventional hydraulic turbine runners that are well known to one skilled in the art, are the Francis and Kaplan turbines which are illustrated schematically in FIGS. 1 and 2 respectively. It should be understood that the discrete turbine blades, runner hub, and other elements of the Francis and Kaplan turbines illustrated in FIGS. 1 and 2 are in the same dimensional relationships and proportions as in well known conventional Francis or Kaplan turbines.
The Francis turbine identified at 10 in FIG. 1, is housed in a scroll case 12, and is characterized by a large number of relatively short, discrete blades 14 spaced circumferentially around the turbine hub. The blades convert hydraulic energy to mechanical energy in a relatively short axial length identified as L in FIG. 1. The axial length L represents the axial distance between the uppermost portion of the blade leading edge 16 and the lowermost tip of the trailing blade edge 18. The blades have a leading edge 16 with a leading edge length, LE, and a trailing edge 18. The maximum diameter of the Francis turbine identified as, D, in FIG. 1 is twice the radial distance between the outermost portion of a blade and the center of rotation of the turbine runner. The axial length L is typically about 1/3 of the maximum diameter D.
Fluid flows through the Francis turbine in the direction of arrows 20 and passes from the blade leading edge 16 to the blade trailing edge 18 of the blades 14.
Turning to FIG. 2, Kaplan turbines are propeller-type turbines in which the positions of the runner blades are adjustable. The conventional Kaplan turbine, identified generally at 30 is substantially enclosed by scroll case 32. The Kaplan turbine includes a plurality of blades 34 each having a leading edge 36 and a trailing edge 38. Like the Francis turbine, the Kaplan turbine has an axial blade length, L, equal to the distance between the uppermost portion of the leading blade edge 36 and the lowermost tip of the trailing blade edge 38; a maximum diameter D equal to twice the lateral distance between the axis of rotation and the outermost blade edge; and a leading edge length LE. In the Kaplan turbine shown in FIG. 2, the axial length L is about 1/4 of the maximum diameter D.
Some of the significant physical attributes and dimensional relationships associated with the Francis and Kaplan turbines illustrated in FIGS. 1 and 2 are; A) in both the Kaplan and Francis turbines, the ratio equal to L/D is less than 0.6; and B) both turbine runners have a significant number of blades each with leading edge lengths LE, such that the ratio of the sum of the lengths of the leading edges , .SIGMA.LE, to the maximum diameter, D, for both turbine runners is equal to or greater than 1. For example, both the Kaplan and Francis turbines have at least four blades and the Francis turbine may have as many as 15 blades.
It should be understood that the foregoing general physical attributes and dimensional relationships associated with the Francis and Kaplan turbines also exist in other conventional turbine runners. The Kaplan and Francis turbines are used herein to highlight generally the foregoing physical attributes and dimensional relationships in conventional turbine runners, because of the relative familiarity of the Francis and Kaplan turbines to one skilled in the art.
The Francis and Kaplan turbines are frequently utilized to generate power in hydroelectric power stations which are typically located along a river. The Francis and Kaplan turbines are located in river power houses, and the river water passes downstream through them, thereby generating the required hydroelectric power.
Use of conventional turbine runners in river power houses has resulted in a certain mortality of fish that travel along rivers and through the river dams. The mortality of the fish traveling through conventional turbines is a result of any one or a combination of the following: internal injuries produced by sudden pressure reductions; the effects of cavitation; injuries from shear due to the presence of velocity gradients; and trauma resulting from contact between the fish and the turbine runner or other turbine component parts.
Contact injury to fish is also the result of leading edge blade strike. Turbine characteristics which may be related to contact injury are flow velocity relative to the blades, the number of blades, the shape of the flow passage, and the spacing of the blades. The relatively large number of blades and total length of the leading edges of the blades (.SIGMA.LE) associated with the Kaplan and Francis turbines and other conventional turbines may contributes to fish mortality as a result of contact between the leading blade edges and the fish. Abrasion damage to fish results from fish being drawn into narrow gaps between turbine blades and other turbine components.
High velocity zones or high velocity gradients (shear) exist at the gaps between rotating and stationary components. Such high velocity shear zones are formed for example, between the blade edges and the throat ring (see item 100 in FIG. 2). The high velocity gradients in the Francis and Kaplan turbines are related to the small axial distance, L, between the leading and trailing edges of the blades.
Cavitation occurs when the local pressure is low enough to cause water vapor bubbles to form, and the downstream implosion of these bubbles occurs when the pressure is sufficiently increased. The implosion produces pressure waves of instantaneous high pressure which are believed to cause fish injury. Conditions which may affect cavitation include: 1) general or local low pressure zones; 2) high velocity zones; 3) abrupt changes in flow direction; 4) surface roughness of the runner and blades; and 5) the air content of the water.
Pressure damage results from rapid decreases in the pressures to which fish have become acclimated. The relatively small ratio of axial length, L, to maximum diameter, D, and the short distance between the leading and trailing edges of the blades in known turbines contributes to fish mortality caused by sudden pressure reductions.
Shear injury to fish passing through a turbine occurs in the zones between streams of water having different velocities. Fish are injured when different parts of their bodies are subjected to different velocities and drag forces.
Existing hydraulic turbines used for hydroelectric power generation have been designed with little regard to their effect on fish which may pass through the turbine. The result is fish mortality in many installations. This is particularly a problem on some rivers where there are a series of hydroelectric facilities along the river and the cumulative fish mortality rate is higher.
The foregoing illustrates limitations known to exist in present hydraulic turbine runners and the turbines in which they are used. Thus, it is apparent that it would be advantageous to provide a hydraulic turbine runner that decreases fish mortality. Accordingly, a suitable alternative hydraulic turbine runner is provided, including features more fully disclosed hereinafter.